A n instruments offers bourdon tube pressure gauges. Elastic pressure gauges indicate the relative difference between the pressure of the medium and the surrounding atmosphere. The construction is simple and robust; no additional source of energy is needed for its operation. Among the existing types of sensing/elastic elements, the most commonly used are bourdon tube pressure gauges. These are used for measurement of pressure and vacuum and are suitable for all clean and non-clogging liquid and gaseous media. The bourdon tube is a thin walled tube of oval cross section, which may be of `c` form or spirally wound. This tube expands when pressure is applied internally; this expansion is converted into rotation of a concentic pointer with a gear movement. The reading indicated on a dial by the pointer is proportional to the pressure applied. C-type bourdon tubes are used for low pressure rnages and helical/spiral tubes for higher pressure ranges.
